The present invention relates to a pneumatic tire having an improved durability, a method for producing the same, and a cushion rubber suitable for use in the pneumatic tire.
Pneumatic tires are generally provided with cushion rubbers between a carcass and each of axial edge portions of a belt layer, as disclosed in JP-A-2002-160508 and JP-B-3370282. The cushion rubbers have an adequate flexibility and serve to ease a strain in the vicinity of the axially edge portions of the belt layer which are largely deformed at the time of running under load.
In general, a cushion rubber has been formed by continuously extruding a rubber compound into a ribbon-like cushion rubber “b” having an approximately triangular cross section, as shown in FIG. 9(A), from a die of an extruder, cutting the extruded cushion rubber “b” to a length corresponding the circumferential length of a tire and, as shown in FIG. 9(C), annularly winding the cut cushion rubber “b” on the outer surface of a carcass ply (not shown) wound around a cylindrical forming drum D. FIG. 9(B) shows a side view of the cut cushion rubber “b” whose both ends b1 and b2 in the circumferential direction of a tire are diagonally cut in the same direction into a tapered form.
The tapered both ends b1 and b2 are jointed so that the thickness t1 of a joint portion J becomes identical with the thickness t2 of the remaining portion, but it is not easy to form a joint portion J having exactly the same thickness as that of the remaining portion. Thus, such a joint portion J having a different thickness may deteriorate the uniformity of a tire. Further, in case of heavy duty tires used for trucks and buses, since the tires are used under conditions of high load and high inner pressure, a strain is easy to concentrate particularly at the joint portion J having a different thickness of the cushion rubber. Therefore, such a joint portion J may cause deterioration of the durability of tires.
It is an object of the present invention to provide a pneumatic tire having no disadvantages caused by joint portion of the cushion rubber.
A further object of the present invention is to provide a pneumatic tire having improved uniformity and durability by forming a cushion rubber having no joint portion J.
Another object of the present invention is to provide a method for producing a pneumatic tire which can eliminate the disadvantages caused by joint portion of the cushion rubber.
These and other objects of the present invention will become apparent from the description hereinafter.